The present invention relates to tires. More particularly, it relates to a tire comprising a specific arrangement of the cords of the carcass-type reinforcement structure in the sidewalls, allowing the obtainment, on the one hand, under substantially normal pressure, of flexible sidewalls capable of imparting particularly favourable qualities, in particular of comfort and rolling resistance, and, on the other hand, under reduced pressure, of rigidified sidewalls capable of bearing the load on the tire, within certain limits.
For some years, tire manufacturers have been devoting considerable effort to developing original solutions to a problem dating back to the very first time use was made of wheels fitted with tires of the inflated type, namely how to allow the vehicle to continue on its journey despite a considerable or total loss of pressure in one or more tires. For decades, the spare wheel was considered to be the sole, universal solution. Then, more recently, considerable advantages have become apparent which may lead to the elimination thereof. The concept of “extended mobility” is being developed. The associated techniques allow travel to continue with the same tire, within certain limits, after a puncture or a drop in pressure. This allows the driver to travel to a repair point, for example, without having to stop, often in dangerous circumstances, to fit the spare wheel.
Two major types of extended mobility technology are currently available on the automobile market. On the one hand, there are tires of the self-supporting type (often known by their English abbreviation ZP, standing for “zero pressure”). Self-supporting tires are capable of bearing a load under reduced pressure, or indeed without pressure, thanks to sidewalls which are reinforced, most frequently by means of inserts of rubber material provided in the sidewalls. The structural rigidity of the sidewalls of a tire of this type is very high. Reinforced sidewall technologies favour operation in degraded mode, normally exceptional or at the very least very occasional for the vast majority of vehicles, to the detriment of everyday operation, which suffers the drawbacks intrinsic to the principle of reinforced sidewalls. In normal operation, at rated service pressure, this may entail considerable disadvantages in terms of rolling resistance and comfort. Furthermore, the strong tendency for the bottom zone of the tire to want to slide out of the rim under the effect of sidewall sagging may limit the impact of this solution.
On the other hand, wheels are available which are equipped with supports capable of supporting the inside of the tread of a tire in the event of sagging of the sidewalls following a drop in pressure. This solution is advantageously combined with a tire comprising a bottom zone capable of minimising the risk of the tire sliding out of the rim. This solution is advantageous since it makes it possible to keep substantially intact the characteristics of travel under normal conditions. On the other hand, it exhibits the drawback of requiring an additional component, the support, for each of the wheels of the vehicle.